Since feet are the foundation on which the rest of the body is supported, foot misalignment can cause many forms of discomfort and disorders. The ligaments and muscles connect the various bones and joints. When weight bearing, the foot, leg, and hip form a closed kinetic chain. Changes in one area will affect all the other areas. This means that a small difference in alignment of foot position or foot motion can have significant effect on the rest of the lower body. So-called functional orthotics can be used to realign the foot relative to the supporting surface and the foot relative to the rest of the body during a gait. These devices are called upon to solve difficult problems in a complex area of anatomy, physiology, and biomechanics.
Functional orthotics are devices usually made by a podiatrist. They often involve a forefoot post that is a raised area on the underside of the orthotic. A problem however, is that there is no exact methodology of being confident that the foot is aligned to provide the desired clinical benefit. Proper posting prevents excessive motion as a compensation for structural problems in the foot. Functional orthotics with podiatrist prescribed posts have the problem that they are fixed and can only be changed by the doctor grinding off or gluing on material. Since the foot in motion is such a complicated system, prescribing and devising these functional orthotics is not yet an exact science and can require multiple visits to get to the point of providing relief for a patient. If a patient has specialized needs for particular activities such as running or golfing, that could require a second, differently shaped orthotic with its own set of multiple visits in order to be produced correctly.
With a mass produced orthotic there are generally no posts at all because there are so many different foot types that one set of fixed posts could not possibly work on the myriad of foot types. Furthermore, many orthotics are made of relatively soft materials that, while better tolerated, have very limited capabilities of resisting ground reactive forces and thus have limited ability to realign foot positions during the execution of a gait.